Absolute Rate Theory for Isolated Systems and the Mass Spectra of Polyatomic Molecules

Rosenstock, H. M.; Wallenstein, M.B.; Wahrhaftig, Austin L.; Eyring, Henry

doi:10.1073/pnas.38.8.667

Cited by 759 publications

(181 citation statements)

References 7 publications

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“…The predominant fragment formed for these derivatives was the same as that for N-phenylglycine (loss of 46 Da) as described by the proposed scheme in Table 2. Thus, these data are consistent with a concept implicating the importance of electronegativity in determining fragmentation rates and mechanisms [13,37,38].…”

Section: Experimental Sy ϭ Intensitypsupporting

confidence: 79%

CE₅₀: Quantifying collision induced dissociation energy for small molecule characterization and identification

Kertesz

Hall

Hill

et al. 2009

J. Am. Soc. Mass Spectrom.

102

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Survival yield analysis is routinely used in mass spectroscopy as a tool for assessing precursor ion stability and internal energy. Because ion internal energy and decomposition reaction rates are dependent on chemical structure, we reasoned that survival yield curves should be compound-specific and therefore useful for chemical identification. In this study, a quantitative approach for analyzing the correlation between survival yield and collision energy was developed and validated. This method is based on determining the collision energy (CE) at which the survival yield is 50% (CE 50 ) and, further, provides slope and intercept values for each survival yield curve. In initial experiments using a defined set of homologous compounds, we found that CE 50 values were easily determined, quantitative, highly reproducible, and could discriminate between structural and even positional isomers. Further analysis demonstrated that CE 50 values were independent of cone potential and orthogonal to compound mass. Experimentally determined CE 50 values for a diverse set of 54 compounds were correlated to Molconn molecular structure descriptors. The resulting model yielded a statistically significant linear correlation between experimental and calculated CE 50 values and identified several structural characteristics related to precursor ion stability and fragmentation mechanism. Thus, the CE 50 is a promising method for compound identification and discrimination. S urvival yield analysis was initially developed as a tool to quantify the distribution of precursor ion internal energies to explain fragmentation patterns that occur using mass spectrometry [1]. Survival yield has since been used as a method to correlate conditions in the mass spectrometer to the energetics of sample ions. These studies have developed a wide array of equations for understanding molecular decomposition in a mass spectrometer. The quasi-equilibrium theory of a unimolecular reaction indicates that the rate of molecular decomposition, as occurs in collision induced dissociation (CID), is dependent on the molecule's internal energy (E), activation energy (E 0 ), number of vibrational degrees of freedom (n), and the entropy of the reaction transition-state (⌬S*). E 0 , n, and ⌬S* are dependent on the structure of the molecule [2], whereas E is a function of the kinetic energy applied to the molecule in the collision cell. The fraction of a precursor molecule that survives a CID reaction (survival yield) depends on the reaction rate and the reaction time in the collision cell. In CID, transferring a portion of the kinetic energy of the accelerated precursor ion to internal energy by collisions with relatively stationary gas atoms increases the internal energy of a sample ion. The maximum energy available for absorption (E com ) by the precursor ion in the collision process is described by eq 1 [3]:where, E com is the center of mass kinetic energy, m G is the mass of the collision gas, E kin is the kinetic energy of the sample ion, and m i is the mass of t...

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Section: Experimental Sy ϭ Intensitypsupporting

confidence: 79%

CE₅₀: Quantifying collision induced dissociation energy for small molecule characterization and identification

Kertesz

Hall

Hill

et al. 2009

J. Am. Soc. Mass Spectrom.

102

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“…The quasi-equilibrium theory (QET) (17,18), nowadays recognized as equivalent to the statistical, or Rice, Ramsperger, Kassel, Marcus (RRKM), theory, assumes that any excess energy in the molecule is first equipartitioned amongst all degrees of freedom. Then, a f luctuation localizes sufficient energy in the coordinate that needs to be broken.…”

mentioning

confidence: 99%

An electronic time scale in chemistry

Remacle

Levine

2006

Proc. Natl. Acad. Sci. U.S.A.

396

335

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Ultrafast, subfemtosecond charge migration in small peptides is discussed on the basis of computational studies and compared with the selective bond dissociation after ionization as observed by Schlag and Weinkauf. The reported relaxation could be probed in real time if the removal of an electron could be achieved on the attosecond time scale. Then the mean field seen by an electron would be changing rapidly enough to initiate the migration. Tyrosine-terminated tetrapeptides have a particularly fast charge migration where in <1 fs the charge arrives at the other end. A femtosecond pulse can be used to observe the somewhat slower relaxation induced by correlation between electrons of different spins. A slower relaxation also is indicated when removing a deeper-lying valence electron. When a chromophoric amino acid is at one end of the peptide, the charge can migrate all along the peptide backbone up to the N end, but site-selective ionization is probably easier to detect for tryptophan than for tyrosine.attosecond lasers ͉ charge transfer ͉ protein mass spectrometry A chemical rearrangement occurs when atoms in a molecule change their specific arrangement. The time scale of chemistry is therefore the time scale for the motion of atoms (1, 2). The forces operating on the atoms determine the path of this motion. In the Born-Oppenheimer approximation, it is the averaging over the much faster motion of the electrons that specifies the potential energy and hence the forces. The physical picture for this approximation is that the electrons instantly adjust to the current position of the nuclei so that the equilibrium arrangement of the bonded atoms is determined as a minimum of the electronic energy. In the Born-Oppenheimer approximation, the system is confined to be in a single stationary electronic state, and if this confinement is strict then there is no electronic time scale that is relevant to chemistry. During a chemical rearrangement, the motion of the atoms can be accompanied by a reorganization of the electronic structure, and recent experimental progress allows for probing this change (3) in real time. However, it is the motion of the nuclei that sets the time scale because the electronic reorganization exactly tracks the shifts in the positions of the nuclei. As the heavier nuclei move, the light electrons immediately adapt.It is recognized that the energy of the same stationary electronic state can have two distinct minima, where the electronic charge distribution has a quite different character. At the immediate vicinity of either of the two configurations of the nuclei, the motion is bounded, but larger-amplitude motion can connect the two hollows. Major intramolecular charge reorganization follows upon a change in nuclear geometry (4-8). The time scale of the charge shuffling is that of the motion of the nuclei relocating between the two configurations.Optical excitation can prepare a nonstationary state, and such a state is often known as the optically bright state. The optically bright state is not sta...

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“…The intermolecular and intramolecular complexes preferentially dissociate to X − + CH 3 Y and isomerize to XCH 3 -Y − , respectively. This model for the X − -CH 3 Y non-RRKM dynamics is consistent with the lifetime and/or lifetime distribution of X − -CH 3 Y dissociation following X − + CH 3 Y association [63,65,[67][68][69], the dissociation dynamics following excitation of the intermolecular and intramolecular modes of X − -CH 3 Y [39,70], and the recrossing dynamics of the [X-CH 3 …”

Section: Comparison Of the Simulation Results With Models For Intrinsmentioning

confidence: 60%

“…Rice-Ramsperger-Kassel-Marcus (RRKM) theory [1][2][3], derived from classical mechanics [3][4][5], is a limiting model for the dynamics of unimolecular decomposition. It assumes that the classical dynamics is ergodic on the time-scale of the unimolecular reaction so that a microcanonical ensemble of states is maintained for the molecules as they decompose [5].…”

Section: Introductionmentioning

confidence: 99%

Models for Intrinsic Non-RRKM Dynamics. Decomposition of the SN2 Intermediate Cl––CH3Br

Paranjothy

Sun

Paul

et al. 2013

Zeitschrift Für Physikalische Chemie

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Chemical dynamics simulations, based on both an analytic potential energy surface (PES) and direct dynamics, were used to investigate the intrinsic non-RRKM dynamics of the Cl products were fit with multi-exponential functions. The intrinsic non-RRKM dynamics is more pronounced for the simulations with the analytic PES than by direct dynamics, with the populations for the former and latter primarily represented by tri-and bi-exponential functions, respectively. For the analytic PES and direct dynamics simulations, the intrinsic non-RRKM dynamics is more important for the isomerization pathway to form ClCH 3 -Br − than for dissociation to Cl − + CH 3 Br. Since the decomposition probability of Cl − -CH 3 Br is non-exponential, the Cl − -CH 3 Br unimolecular rate constant depends on pressure, with both high and low pressure limits. The high pressure limit is the RRKM rate constant and for the simulations with the analytic PES the rate constant decreased by a factor of 3.0, 5.6, and 4.3 in going from the high to low pressure limit for total energies of 40, 60, and 80 kcal/mol. For the direct dynamics simulations these respective factors are 2.4, 1.4, and 1.2. A separable phase space model with intermolecular and intramolecular complexes describes some of the simulation results, but overall models advanced for intrinsic non-RRKM dynamics give incomplete representations of the intermediate and product populations vs. time determined from the simulations.

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Absolute Rate Theory for Isolated Systems and the Mass Spectra of Polyatomic Molecules

Cited by 759 publications

References 7 publications

CE₅₀: Quantifying collision induced dissociation energy for small molecule characterization and identification

CE₅₀: Quantifying collision induced dissociation energy for small molecule characterization and identification

An electronic time scale in chemistry

Models for Intrinsic Non-RRKM Dynamics. Decomposition of the SN2 Intermediate Cl––CH3Br

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Absolute Rate Theory for Isolated Systems and the Mass Spectra of Polyatomic Molecules

Cited by 759 publications

References 7 publications

CE50: Quantifying collision induced dissociation energy for small molecule characterization and identification

CE50: Quantifying collision induced dissociation energy for small molecule characterization and identification

An electronic time scale in chemistry

Models for Intrinsic Non-RRKM Dynamics. Decomposition of the SN2 Intermediate Cl––CH3Br

Contact Info

Product

Resources

About

CE₅₀: Quantifying collision induced dissociation energy for small molecule characterization and identification

CE₅₀: Quantifying collision induced dissociation energy for small molecule characterization and identification